Method of adjusting the pH of a pretreatment solution using carbon dioxide useful for integrating saccharification and fermentation of a biomass

Abstract

The present invention provides for a method of fermenting or saccharifying a biomass comprising: (a) (i) contacting a biomass comprising a polysaccharide, and an ionic liquid (IL) to form a first solution, or (ii) providing the first solution comprising the biomass and the IL, (b) contacting the first solution and carbon dioxide such that the first solution results in a lower pH, (c) introducing (i) an enzyme capable of enzymatically to breakdown at least one bond in the polysaccharide or a breakdown product of the polysaccharide, and/or (ii) a microorganism that capable of producing the enzyme and/or fermenting the polysaccharide or a breakdown product of the polysaccharide, such that the polysaccharide is at least partially broken down and the first solution is transformed into a second solution.

What is claimed is: 
     
       1. A method of saccharifying and fermenting a biomass comprising:
 (a) (i) contacting a biomass comprising a polysaccharide, and an ionic liquid to form a pre-treated biomass solution, or (ii) providing the pre-treated biomass solution comprising the biomass and the ionic liquid, wherein the ionic liquid is a cholinium-based amino acid ionic liquid, and wherein the pH of the pre-treated biomass solution ranges from 12 to 14; 
 (b) contacting the pre-treated biomass solution and gaseous carbon dioxide such that the H of the pre-treated biomass solution ranges from 4.5 to 7.5, wherein the gaseous carbon dioxide has a pressure ranging from 0.1 MPa to 2 MPa, thereby forming a pH-adjusted pretreated biomass solution; 
 (c) (i) introducing directly to the pH-adjusted pre-treated biomass a cellulase, a hemicellulase, or a mixture of a cellulase and a hemicellulase, such that the polysaccharide is broken down, thereby forming a hydrolyzed biomass, and (ii) combining the hydrolyzed biomass with a microorganism for fermentation at a temperature ranging from room temperature to 37° C.; 
 (d) optionally separating a solid portion and a liquid portion of the hydrolyzed biomass second solution; and 
 (e) optionally recovering the ionic liquid from the liquid portion of the hydrolyzed biomass. 
 
     
     
       2. The method of  claim 1 , wherein the contacting step (a) comprises heating the biomass and the ionic liquid at a temperature ranging from room temperature to 150° C. 
     
     
       3. The method of  claim 1 , wherein the biomass is a biomass derived from a hardwood feedstock, a softwood feedstock, a grass feedstock, or an agricultural waste feedstock, algal biomass, municipal solid waste, food processing waste, or a mixture thereof. 
     
     
       4. The method of  claim 1 , wherein the cholinium based amino acid ionic liquid is selected from cholinium lysinate, cholinium glutamate, or cholinium aspartate. 
     
     
       5. The method of  claim 1 , wherein the ionic liquid is pure ionic liquid, is in an aqueous ionic liquid system, or is an ionic liquid/solvent mixture. 
     
     
       6. The method of  claim 5 , wherein the concentration of the ionic liquid in the aqueous system ranges from 0.1-50% 100 wt %. 
     
     
       7. The method of  claim 1 , wherein the enzyme is a cellulase. 
     
     
       8. The method of  claim 1 , wherein the microorganism is a yeast or a prokaryote. 
     
     
       9. The method of  claim 8 , wherein the prokaryote is a  Zymomonas, Streptomyces, Clostridium, Klebsiella, Ralstonia, Bacillus, Pseudomonas , or  Escherichia.    
     
     
       10. The method of  claim 1 , wherein the contacting step (a) is repeated with a fresh biomass and the ionic liquid used comprises in part at least some of the ionic liquid recovered from the recovering step (e). 
     
     
       11. The method of  claim 10 , wherein the method steps are repeated for a plurality of times wherein for each contacting step (a), except for the first time contacting step (a) takes place, the ionic liquid used comprises in part at least some of the ionic liquid recovered from the recovering step (e). 
     
     
       12. The method of  claim 1 , wherein the separating step (d) occurs immediately subsequent to the recovering step (e). 
     
     
       13. The method of  claim 1 , wherein the method results in glucan, xylan, lignin, or a mixture thereof in the solid portion of the second solution. 
     
     
       14. The method of  claim 1 , wherein the method results in a hexose or oligomer thereof, a pentose or oligomer thereof, ethanol, or a mixture thereof in the liquid portion of the second solution. 
     
     
       15. The method of  claim 1 , wherein the method further comprises a releasing step comprising releasing carbon dioxide by either elevating the temperature or introducing nitrogen gas, or both. 
     
     
       16. The method of  claim 1 , wherein the yield of glucose from the biomass is >85%. 
     
     
       17. The method of  claim 1 , wherein the yield of xylose from the biomass is >65%.